Emotiva CMX-2 Line conditioner and DC offset filter. Review by Tim Smith

Like many of you, I have experienced the hum of tube amp transformers. Like many of you, I have assumed that this was normal–the price of SET amps, a minor trade-off for that magical tube sound. Normally the hum is not noticeable unless one is within a couple feet of the amp. With headphone amps the hum is much more of an issue; it will bleed its way into your ears.

Those of you with Marantz CD players may even hear a bit of hum coming from your CD5003 or 5004. Well, no more. To be sure, some components and tube amps will hum no matter what sort of line conditioning you throw at them. To see just where the root of the problem lies, why not try this $99 USD marvel? (With shipping, duties and exorbitant ‘brokerage’ fees, this unit will cost about $180 CDN.)

The CMX-2 is worth every penny. I have had one for three months. I can assure you that it will not rob your system of dynamics. It will eliminate hum and high frequency noise too. It has completely eliminated transformer hum on all five tube amps currently in the house. And it has done the same for my Marantz CD players. This suggests that the problem is my dirty power line. I have DC offset on the AC line.

About a year ago, I had a Decware CSP2+ on loan from a dealer. It was so frighteningly good with my Beyerdynamic T1s, I decided to sell my T1s. That might seem counterintuitive. Here is my rationale: that amp was so amazing, I was worried that I would listen too long, too loud. Having invested so much in my main rig, did I really want to be distracted from it by this world-class headphone set-up? Also, there was a tiny bit of hum from the Decware that bothered me, since I tend to listen to solo piano and guitar music when I am multi-tasking. Such music is full of empty spaces just waiting to be filled by hum. Today I wonder if that Decware would still be in the house had I plugged it into the Emotiva CMX-2. Perhaps the temptation to keep it would have been too strong.

You see, I just plugged a Woo Audio WA6 SE (on review from Brosseau Audio in Quebec) into the Emotiva CMX-2. Now it is dead quiet. There had been a tiny bit of hum. Not enough to bother me, but it was noticeable with my Jamie Summers ear. Not only is the hum gone, but all the noise from my digital player too.

As Emotiva’s website says, “DC offset is usually the result of unbalanced loads or by flaws in the power distribution system itself. It can cause DC current flow in the transformers that power your audio equipment” causing them to hum. “The CMX-2 delivers clean power, free of high-frequency line noise and potentially audible DC offsets to your audio components. It also continuously monitors your AC power line wiring integrity and alerts you to common fault conditions like open grounds and reversed lines.” The CMX-2 also uses common mode and differential mode L-C filtering to fight high-frequency noise.


HiFiMan, Marantz, Bottlehead, DH Labs-Connex, Emotiva

As I write this, Diana Krall’s SACD “Love Scenes” is playing through a Marantz SA-8003 feeding a Woo Audio WA6 SE, powering HiFiMan HE-400s decked out with Audio Sensibility Impact SE 7N OCC copper cables. This disc can be a bit sibilant but the Emotiva seems to have tamed that without reducing the bite and attack of Christian McBride’s bass. Russell Malone’s guitar is as smooth as silk. I can hear every little breath Diana Krall takes.

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I have just inserted Glen Campbell’s “Wichita Lineman.” The DC offset is not still on the line. His Fender VI is crisp, resonant, with extra bite.

The CMX-2 eliminated the transformer hum on my Line Magnetic 518i a. It solved the issue for all three of my Musical Paradise tube amps. Through the LM amp, I have listened to everything from Stravinsky to Led Zeppelin. There is no loss of power. Techno rocks the house just as it did with my amps plugged straight into the wall. This little device is so good, I just bought a second one for my second system. Another home run for Emotiva, a company making good-sounding products at down-to-earth prices. Highly recommended.


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3 Comments on Emotiva CMX-2 Line conditioner and DC offset filter. Review by Tim Smith

  1. Any experience with the Blue Circle RPD-15? I’m looking at one of these to help with some nasty noise from the tranny of a Coincident Turbo 845 SE. Just don’t want to compromise sonics, as it rocks aside from this quirk.

  2. Did nothing for my ground loop hum coming out of the subwoofer. 3 to 2 ground lift adapter worked to temporarily test the issue. Glad this works for some people but not for me. All it turned out to be is an expensive surge protector with only two outlets.

    • Did you even read the article? This device will do nothing (and is not supposed to do anything) for ground loops. Its purpose is literally in the name: “DC offset”.

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